Mechanochemical treatment boosted microwave-assisted sulfonation of softwood lignin for the fabrication of dye dispersant

Utilizing industrial lignin, which has the features of high yield and low added value, as a raw material for dye dispersants can produce significant environmental benefits and promote the sustainable development of resources. Ingeniously, we investigated the mechanochemical method to enhance effect in microwave-assisted sulfonation and the preparation of lignin-based dye dispersant using epichlorohydrin cross-linking. The results showed that lignin ball milling with Na 2 SO 3 could significantly increase the amount of C–O active structures and enhance its sulfonation reactivity. Under a lignin/Na 2 SO 3 ratio of 1:1, the charge density of the sulfonated lignin (milled lignosulfonate, MLS) achieved through microwave-assisted sulfomethylation up to 1.87 meq/g. Notably, the charge density of lignosulfonate (milled epichlorohydrin-cross-linked lignosulfonate, MELS) obtained by cross-linking with epichlorohydrin reached 1.91 meq/g with a degree of substitution of 1.45 mmol/g and molecular weight of 10530 g/mol. As compared with two commercial lignosulfonates and MLS, MELS displayed the greatest dispersion stability, increased the dyeing rate and K/S λmax value of dyed fiber while reducing staining. This work paved a new avenue for lignin valorization and provided new insights into the fabrication of lignin-derived dye dispersant.